Chapter 3 - Techniques for Stable Isotope Analysis of Fluid and Gaseous Inclusions

Abstract

This chapter discusses the analysis of fluid and gaseous inclusions by stable isotope techniques. The choice of the method of extraction depends on the mineral hosting the inclusions and the fluid characteristics. Crushing and decrepitation are complementary methods having limitations, such as the generally inability to separate different generations of inclusions. Analysis of individual inclusions has only recently been made successfully using a laser GC system. Several attempts have been made using Raman microprobe, based on the relationship among the different isotopic peaks for CO2 and the isotopic ratios of the carbon species. The measured isotopic ratios for a single fluid inclusion using Raman spectroscopy are precise, but inaccurate due to varying sample geometry, depth to inclusion and thickness. Thus, the results of this method are unsatisfactory. Sharp et al., (2001) developed a method for microliter water analysis based on carbon reduction, merging the advantages that gas chromatography and continuous flow technology provide for mass spectrometric analysis techniques.. Stable isotope analysis of fluid inclusions involves two separate steps, namely, quantitative extraction of fluid phase from the host mineral and mass spectrometric analyses of the extracted phase. The least ambiguous analyses can also be performed on macroscopic fluid inclusions. In this way different generations of inclusions can be analyzed.